The biosphere is the envelope of Earth in which life is found: plants, animals, fungi, micro-organisms and the environment they live in. Together with the lithosphere, atmosphere and hydrosphere it forms the geographical envelope. Natural zones are the most visible pattern of the geographical envelope. Exams ask you to recognise zones by climate, soils and vegetation, to understand altitudinal zonation and to know the hierarchy of geosystems.
§1. The biosphere and the role of living matter
The theory of the biosphere was developed by V. I. Vernadsky. He called the sum of all living organisms living matter and showed that it is a force that reshapes the face of the Earth. Limits of the biosphere: in the atmosphere roughly up to the ozone layer (only spores of micro-organisms are found there), in the hydrosphere through its whole depth down to the ocean floor, and in the lithosphere down to a few kilometres. Life is densest in the thin "film of life" where the envelopes meet: the land surface, the soil and the sunlit upper layer of the ocean. Functions of living matter:
Energy — green plants store solar energy through photosynthesis;
Gas — atmospheric oxygen is mainly a product of plant activity;
Concentration — organisms accumulate calcium, silicon and other elements (this is how limestone, coal and peat formed);
Soil formation — soil is the joint product of rock, climate and organisms.
Substances move in a biological cycle: plants (producers) make organic matter, animals (consumers) eat it, and micro-organisms (decomposers) break down remains and return minerals to the soil.
Worked example
In a food chain about 10% of the energy passes to each next link. Plants have stored 10,000 kJ. How much reaches the second-order consumers (predators)?
Plants → herbivores: 10,000 · 0.1 = 1,000 kJ.
Herbivores → predators: 1,000 · 0.1 = 100 kJ.
Answer: about 100 kJ — which is why there are far fewer predators than herbivores.
§2. The geographical envelope and its laws
The geographical envelope is the integrated shell in which the lithosphere, atmosphere, hydrosphere and biosphere interpenetrate and interact. Its main laws are:
Integrity — a change in one component changes the others (cut a forest and the soil is washed away, river regimes are upset and the climate becomes drier).
Cycling of matter and energy — the water, oxygen and carbon cycles.
Rhythm — daily and yearly changes (day and night, seasons).
Zonality — the regular change of natural complexes from the equator to the poles, based on the balance of heat and moisture. The theory of zonality is linked with V. V. Dokuchaev, the founder of soil science.
Azonality — the disruption or modification of zonality by relief, distance from the ocean and ocean currents.
Examples of azonality: the coastal Atacama and Namib deserts lie beside the ocean in the tropics because of cold currents; deep inside Eurasia steppe and desert replace forest because the ocean is far away; in mountains altitudinal belts appear instead of latitudinal zones. Real nature is always the joint result of zonal and azonal factors.
Hierarchy of geosystems: geographical envelope → continents and oceans → physiographic countries → natural zones → landscapes
§3. Natural zones
A zone is a large area with similar climate, soils, plants and animals. From the equator to the poles:
Wet equatorial forest — hot and wet all year, many-layered evergreen forest, red-yellow ferrallitic soils (Amazonia, the Congo basin). Biomass is the greatest, but the soil is thin: organic matter decays fast and is leached by rain.
Savanna — wet summer and dry winter, tall grass and scattered trees (baobab, acacia), red-brown soils; many large grazers (zebras, giraffes).
Tropical desert — the Sahara, the Namib, central Australia; very little rain, a large daily range of temperature, sparse plants.
Hard-leaved evergreen forest and scrub — the Mediterranean; hot dry summer, mild wet winter; brown soils.
Temperate desert and semi-desert — the plains of Central Asia; grey (serozem) and brown soils, ephemeral plants, saxaul.
Steppe — grassy and treeless; the most fertile soil, chernozem (black earth); mostly ploughed.
Broadleaf and mixed forest — brown forest and sod-podzolic soils.
Forest-tundra and tundra — mosses, lichens, dwarf shrubs, permafrost, bogs.
Arctic desert — ice and snow, almost no plants.
Worked example
Features: "hot dry summer, mild wet winter, evergreen hard leaves". Which zone is it?
Rain in winter and drought in summer mean a Mediterranean-type subtropical climate.
Hard leaves are an adaptation to summer drought.
Answer: the zone of hard-leaved evergreen forest and scrub.
§4. Altitudinal zonation
In mountains temperature falls with height and moisture changes, so natural belts follow one another from bottom to top — just as when travelling from the equator to the pole. The number of belts depends on the height of the mountains and their latitude: high mountains near the equator have many belts, low mountains near the poles few. The lowest belt matches the latitudinal zone at the foot. In the mountains of Uzbekistan the belts are: desert → adyr foothills (ephemerals, tulips) → mountain forest (juniper, walnut, maple) → yaylov pastures (subalpine and alpine meadows) → snow and glaciers.
Worked example
Two mountains are the same height (5,000 m): one near the equator, the other at 60° latitude. Which has more altitudinal belts?
Near the equator the foot is in wet forest and all the zones follow one another upwards.
At 60° the foot is already taiga, with only tundra and snow above.
Answer: the mountain near the equator has more belts.
§5. Physiographic regionalisation
Dividing a territory into parts with similar natural features is called regionalisation: continent → country → district → region. Central Asia is a physiographic country of Eurasia, and Uzbekistan within it is divided into physiographic districts. Regionalisation is needed for planning land use, locating farming and protecting nature.
§6. Protecting the biosphere
Human activity strongly affects the biosphere: forests are cleared, land becomes salinised and species disappear. Protective measures include:
Nature reserves (zapovedniks) — areas where nature is fully untouched (in Uzbekistan the Chatkal, Zaamin, Hissar and Nurata reserves, among others);
National parks — protection combined with tourism;
the Red Book — a list of endangered plant and animal species (in Uzbekistan the snow leopard, the Bukhara deer, the goitered gazelle and others).
Vernadsky called a new stage of the biosphere, guided by human reason, the noosphere.
Check yourself
What is the main cause of zonality?
Which zone has podzol soils?
In which zone do the most fertile soils form?
"Geographical envelope → continents → ... → natural zones": what goes in the gap?
What does the number of altitudinal belts depend on?
Plants store 5,000 kJ. How much passes to herbivores under the 10% rule?
Who developed the theory of the biosphere?
Which zone has baobabs and tall grass?
Common mistakes
Confusing altitudinal zonation with latitudinal zonality: one goes from bottom to top in mountains, the other from equator to pole on plains.
Placing savannas in the temperate belt — they are subequatorial.
Treating azonality as a kind of zonality — it is the result of factors that disrupt zonality.
Thinking wet equatorial soils are very fertile — the biomass is huge, but the soil is leached and thin.
Mixing up Vernadsky (biosphere) and Dokuchaev (zonality, soil science).